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Production and emission of CO2 in two unproductive lakes in northern Sweden
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
2009 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

sted, utgiver, år, opplag, sider
Umeå: Institutionen för Ekologi, miljö och geovetenskap, Umeå universitet , 2009. , 28 s.
Emneord [en]
lake, carbon dioxide, organic carbon, inorganic carbon, boreal, arctic, DOC, DIC, CO2, emission, thermal stratification, allochthonous organic carbon
HSV kategori
Forskningsprogram
naturgeografi
Identifikatorer
URN: urn:nbn:se:umu:diva-26967ISBN: 978-91-7264-878-4 (tryckt)OAI: oai:DiVA.org:umu-26967DiVA: diva2:275328
Disputas
2009-12-03, Naturvetarhuset hörsal N450, Johan Bures Väg, Umeå universitet, Umeå, 10:00 (svensk)
Opponent
Veileder
Tilgjengelig fra: 2009-11-12 Laget: 2009-11-04 Sist oppdatert: 2009-11-13bibliografisk kontrollert
Delarbeid
1. Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden
Åpne denne publikasjonen i ny fane eller vindu >>Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden
2007 (engelsk)Inngår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, Vol. 59, nr 5, 797-803 s.Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Unproductive lakes are generally supersaturated with carbon dioxide (CO2) and emit CO2 to the atmosphere continuously during ice-free periods. However, temporal variation of the partial pressure of CO2 (pCO2) and thus of CO2 evasion to atmosphere is poorly documented. We therefore carried out temporally high-resolution (every 6 h) measurements of the pCO2 using an automated logger system in the surface water of a subarctic, unproductive, lake in the birch forest belt. The study period was June–September 2004. We found that the pCO2 showed large seasonal variation, but low daily variation. The seasonal variation was likely mainly caused by variations in input and mineralization of allochthonous organic matter. Stratification depth probably also influenced pCO2 of the surface water by controlling the volume in which mineralization of dissolved organic carbon (DOC) occurred. In lakes, with large variations in pCO2, as in our study lake a high (weekly) sampling intensity is recommended for obtaining accurate estimates of the evasion of CO2.

Identifikatorer
urn:nbn:se:umu:diva-20329 (URN)10.1111/j.1600-0889.2007.00307.x (DOI)
Tilgjengelig fra: 2009-03-18 Laget: 2009-03-18 Sist oppdatert: 2009-11-10
2. Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake
Åpne denne publikasjonen i ny fane eller vindu >>Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake
Vise andre…
2007 (engelsk)Inngår i: Freshwater Biology, Vol. 52, nr 3, 549-560 s.Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal (δ13C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water.

2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m-2 day-1, of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column.

3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.

4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source.

Identifikatorer
urn:nbn:se:umu:diva-11879 (URN)10.1111/j.1365-2427.2007.01725.x (DOI)
Tilgjengelig fra: 2007-03-15 Laget: 2007-03-15 Sist oppdatert: 2009-11-10bibliografisk kontrollert
3. Gas transfer rate and CO2 flux between an unproductive lake and the atmosphere in northern Sweden
Åpne denne publikasjonen i ny fane eller vindu >>Gas transfer rate and CO2 flux between an unproductive lake and the atmosphere in northern Sweden
2008 (engelsk)Inngår i: Journal of Geophysical Research - Biogeosciences, Vol. 113, Art.no. G04006- s.Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Measurements of the gas transfer rate of CO2 between lake water and the atmosphere present a critical problem for the understanding of lake ecosystem carbon balances and landscape carbon budgets. We present calculations of the gas transfer rate of CO2 from direct measurements of the CO2 flux using an eddy covariance system and concurrent measurements of the concentration of CO2 in the surface water in a lake in boreal zone of northern Sweden. The measured gas transfer rate was different, and in general larger than, rates obtained with the most commonly used models for prediction of the gas transfer rate in lakes. The normalized gas transfer rate (k600EC) was well predicted from the wind speed at 10 m height if data were bin classed into wind classes of 1 m/s for winds above 1 m/s. Unbinned data were also correlated to wind speed but also to water temperature, water temperature/air temperature ratio and to incoming photosynthetic active radiation (PAR). These relationships could reflect effects of both physico-chemical reactions and biological activity.

Identifikatorer
urn:nbn:se:umu:diva-11368 (URN)10.1029/2008JG000688 (DOI)
Tilgjengelig fra: 2008-12-16 Laget: 2008-12-16 Sist oppdatert: 2009-11-11bibliografisk kontrollert
4. Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake
Åpne denne publikasjonen i ny fane eller vindu >>Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake
2010 (engelsk)Inngår i: Journal of Geophysical Research, ISSN 0148-0227, Vol. 115, nr G02024, 10PP- s.Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied the variations in surface water CO2 during the ice-free period in the humic Lake Merasjärvi in northern Sweden. Meteorological, hydrological and limnological data were collected using data logging equipment permitting high time-resolution. The surface water of the lake was supersaturated with respect to CO2 throughout the study period. There were, however, considerable diurnal and longer-term temporal variations of the surface water CO2 concentrations. Partial least squares (PLS) models were used to link the logged CO2 data to the multivariate dataset. On the longer-term time scale (analyzed with 24h means of the logged data) high concentrations of surface water CO2 were best related to the depth and temperature of the upper warmer layer (epilimnion), and to erosion of the underlying colder layer (hypolimnion). The diurnal variation (analyzed with 30 minute means of the logged data) was best related to the thermal dynamics within the epilimnion, which regulated the surface water access to CO2 stores within this layer. Variables related to CO2 emission and photosynthesis (wind and PAR), showed only weak correlations to variations of the surface water CO2 concentration. Accordingly, the CO2 flux, measured with the eddy-covariance technique, was not correlated to the surface water CO2 concentration.

Emneord
lake, carbon dioxide, PLS, thermal stratification, boreal
HSV kategori
Forskningsprogram
naturgeografi
Identifikatorer
urn:nbn:se:umu:diva-26965 (URN)10.1029/2009JG001085 (DOI)000279310300001 ()
Tilgjengelig fra: 2009-11-04 Laget: 2009-11-04 Sist oppdatert: 2011-10-17bibliografisk kontrollert

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